Adhesive compositions, particularly conductive adhesives, have recently gained great popularity in the microelectronics industry. These adhesives are used for a variety of purposes with one of the more prominent uses being the attachment of a semiconductor die, dies or chips, to a substrate, or other support medium. One common problem associated with these adhesives is that upon exposure to high temperatures they exhibit a tendency to undergo outgassing, wherein absorbed or occluded gases, formed during the curing of the adhesive, or during subsequent heat aging of the cured adhesive due to thermal instability, are released. This is a critical problem since, all too often, the success or failure of an electrical component is a direct function of the degree of outgassing undergone by the adhesive resulting in void formation within the adhesive, thereby adversely affecting the thermal and electrical properties of the adhesive.
A number of conductive and thermally stable adhesives have been reported. In U.S. Pat. No. 4,147,669, there is disclosed an electrically and thermally conductive adhesive containing an alloy formed by first mixing together gallium and tin to form an eutectic mixture, mixing a powdered metal such as gold, silver or copper with this mixture to form an alloy and then mixing a resin with a curing agent with this alloy. The resin and curing agent disclosed in this patent are any conventional type known to those skilled in the art.
In U.S. Pat. No. 4,311,615, there is disclosed an electrically conductive film comprised of a palladium (II) polyamic acid compound and an appropriate solvent such as N-methyl-2-pyrrolidone or the like. The inventors in the above patent disclose that the conductivity of the adhesive is a function of the presence of the palladium (II) ions.
U.S. Pat. No. 3,073,784 discloses an adhesive composition comprised of an organic diamine and a tetracarboxylic acid anhydride dissolved in an organic solvent. Silver is disclosed as the conductive agent.
U.S. Pat. No. 3,684,533 discloses a screen printable solder composition comprised of an active hydrogen-containing compound selected from the group of hydroxyl substituted aliphatic, mononuclear aromatic or polynuclear aromatic amines, rosin, an organic solvent and a thixotropic agent.
U.S. Pat. No. 3,746,662 discloses a thermally and/or electrically conductive polymerizable dispersion comprised of an epoxy resin, a curing agent, a powdered tough polymer component, and metal particles. The conductivity of the disclosed adhesive is increased by polar groups such as free hydroxyls or carboxyls on the epoxy resin.
U.S. Pat. No. 2,864,774 discloses a conductive composition wherein the conductive properties are attained by the in situ formation of cryptocrystalline metallic particles within a resin composition.
U.S. Pat. No. 3,677,974 discloses an electrically conductive adhesive comprised of 25-35 parts of a novolak-epoxy resin, 65-75 parts of particulate silver and 0.5-1.4 parts by weight of an imizadole curing agent.